[clang] [test] Move RISCV tests to clang/test/CodeGen/RISCV/ (PR #91783)

[Craig Topper via cfe-commits]

https://github.com/topperc approved this pull request.

LGTM. I think most of there were in CodeGen because they are based on aarch64 tests. I guess AArch64 doesn't have its own directory.

https://github.com/llvm/llvm-project/pull/91783